JP2001152290A - High gas pressure contact rail - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a sound gas pressure welded joint by preventing defects attributable to formation of oxide or low melting point composite oxide (mullite) generated at a pressure contact interface during gas pressure welding of rails. SOLUTION: In mass%, C: 0.60 to 1.20%,
Si: 0.20% or less, Mn: 0.40% or less, Cr: 0.01 to 0.20% if necessary,
And Si + Mn + Cr is 0.50% or less, the balance consists of iron and unavoidable impurities, and the hardness is HB220-
A high gas pressure contact rail characterized by being HB300.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pearlitic rail for railway used mainly as a long rail by gas pressure welding.

[0002]

2. Description of the Related Art In recent years, railroad rails have been developed into long rails by welding from the viewpoint of simplifying track maintenance and inspection, suppressing noise and vibration, and improving ride comfort. Welding methods used include flash butt welding, gas pressure welding, enclosed arc welding, and thermite welding.

[0003] Among these welding methods, flash butt and gas pressure welding are essential technologies for elongating rails, as shown in the literature (iron and steel, Vol. 70, No. 10, 1984). It has become. In the case of these joinings, since the rails are joined together, the joining property is easily affected by the rail steel component. Particularly, in gas pressure welding, the end faces to be joined are brought into close contact with each other, and while being pressed in the rail axis direction, in the atmosphere and heated from the outer periphery with an oxygen-acetylene flame and joined, an oxide is easily generated at the joint interface, In some cases, it becomes a multi-component low-melting oxide and becomes a welding defect.

Therefore, several methods have been studied to prevent oxidation during welding. For example, JP-A-7-227
Japanese Patent Publication No. 684 discloses a method for preventing the invasion of oxygen by filling the outer peripheral edge with cover arc welding or the like while pressing and holding the end faces of the bar steel prior to gas pressure welding. Also, Japanese Patent Application Laid-Open No. 7-232285 discloses a method of preventing the invasion of oxygen and attaching the graphite foil to the outer peripheral edge of the bonding surface or sandwiching it between the bonding surfaces, and removing the intruding oxygen by burning carbon. ing. Although these are effective to a certain extent, the addition of steps or materials leads to an increase in working time and costs.

[0005] By the way, conventionally used rail steel is a high carbon steel having a C of 0.6% or more. When the steel is pressed by gas, it is described in the literature (Journal of the Japan Welding Society, Vol. 14, No. 2).
No. 1996), it is believed that the gas pressure weldability is relatively good because the oxide once formed can be reduced by carbon in the steel.

[0006]

SUMMARY OF THE INVENTION Rail steel is a structural member, and it is a material whose strength must be ensured due to its characteristics. Therefore, in most cases, the alloy is manufactured by adding an alloy to iron, and alloys such as Si, Mn, and Cr are generally used as the strengthening elements. However, since these elements are oxide-forming elements, they form oxides at the pressure-welded interface, and during the subsequent pearlite transformation during cooling, these oxides are likely to generate low-strength ferrite using the oxides as nuclei, and the In the case of forcible fracture under stress, a dimple fracture surface, a so-called flat fracture surface, is generated, and the fracture strength is reduced.

[0007] These oxides are combined with the unavoidable Al oxide to form a composite oxide (mullite) having a low melting point (about 1100 ° C), which also causes welding defects. Since the oxide of Al has a low generation energy and is stable, it is not easily reduced by carbon in a temperature range (up to 1300 ° C.) exposed to atmospheric pressure and gas pressure welding.

[0008] In the case of rail steel, in order to prevent the incorporation of Al as much as possible, the deoxidation of steelmaking is performed using A
In many cases, a method other than l-killed is used, but even in such a case, a small amount of Al is unavoidable, and as a result, it may affect the generation of defects during pressure welding. An object of the present invention is to prevent the formation of oxides of Si, Mn, and Cr at a pressure-contact interface, and to obtain good gas-pressure contact properties.

[0009]

SUMMARY OF THE INVENTION The present invention prevents the oxidation of Si, Mn, and Cr at the pressure interface at the time of gas pressure welding of rails, and reduces the production of single oxides and multicomponent low melting point composite oxides. The rails that can be prevented are as follows. (1) In mass%, C: 0.60 to 1.20%,
Si: 0.20% or less, Mn: 0.40% or less, and Si + Mn: 0.50% or less, the balance being iron and unavoidable impurities, and hardness of HB220-
A high gas pressure contact rail characterized by being HB300.

(2) Cr: 0.01% by mass
The high gas pressure contact rail according to the above (1), wherein the high gas pressure welding rail contains -0.20% and Si + Mn + Cr: 0.50% or less. (3) Mo: 0.01 to 0.50% by mass%
The high gas pressure contact rail according to the above (1) or (2), comprising: (4) Further, by mass%, Cu: 0.05 to 1.00.
%, Ni: 0.05 to 1.00%, one or two kinds of which are contained, the high gas pressure contact rail according to any one of the above (1) to (3). (5) In mass%, Nb: 0.005 to 0.05
%, V: 0.01 to 0.20%, Ti: 0.005
The high gas pressure contact rail according to any one of the above (1) to (4), wherein the rail contains at least one kind of at least 0.050%. (6) The high gas pressure contact rail according to any one of the above (1) to (5), further comprising Co: 0.1 to 2.0% by mass%.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The present inventors have focused on the component composition of the rail steel as a means for suppressing the formation of oxides during gas pressure welding, and have reduced the alloying elements for which oxide formation is easy as much as possible.
The present invention is based on the idea that the gas pressure contact property can be improved while maintaining the performance required for the rail by supplementing the alloy element with the hardly oxidizable alloy element.

Hereinafter, the present invention will be described in detail. First, the reasons for limiting the component composition will be described. The component content is% by mass. C is an element that satisfies the strength that the rail should have and that stably forms a pearlite structure to secure wear resistance. For this purpose, the content of 0.60% or more is required. However, if the content is higher than 1.20%, a large amount of cementite structure is precipitated and ductility is remarkably reduced.

Although Si is effective for strengthening ferrite ground in pearlite, it is relatively easy to form an oxide.
l is an element that promotes the formation of a composite oxide with
It is limited to 0.20% or less.

Mn is an element effective for lowering the transformation temperature of pearlite and improving the strength. However, like Si, it is relatively easy to form an oxide and promotes the formation of a composite oxide with Al. Therefore, if it exceeds 0.40%, the effect becomes apparent. Therefore, its content range is 0.40
% Or less.

Cr is an element that stabilizes the pearlite structure and is effective in improving the strength.
The above is added. However, like Si and Mn, oxide formation is relatively easy, and it is an element that promotes formation of a composite oxide with Al.

Further, when the content of Si + Mn or Si + Mn + Cr exceeds 0.50%, oxide formation during gas pressure welding becomes easy, and the formation of a composite oxide with Al is promoted. Limited.

Further, if necessary, Mo, Cu, N
i, Co, Nb, V, and Ti are contained under the following conditions.
Mo is an element that is effective for improving the strength and does not easily form an oxide, and thus does not affect the gas pressure contact property. To improve the strength, 0.01% or more is required. On the other hand, when it exceeds 0.50%, martensite is formed, which is harmful to the surface damage resistance inherent in rail steel.

Since Cu and Ni are effective elements for improving the strength and hardly form an oxide, they do not affect the gas pressure contact property and do not impair ductility and toughness. If the strength is less than 0.05%, the effect will be reduced.
If the content exceeds 1.00%, the effect is saturated. Therefore, each content is in the range of 0.05 to 1.00%.

Nb, V, and Ti are elements that improve the strength by precipitation hardening, but their effects are reduced below the lower limit, and their effects are saturated above the upper limit.
b: 0.005 to 0.05%, V: 0.01 to 0.20
%, Ti: 0.005 to 0.050%.

Co is an element that has the effect of enhancing pearlite generation and does not easily form an oxide, so that it does not affect the gas pressure contact property. 0.1% or more is required for strengthening the pearlite structure. On the other hand, if it exceeds 2.0%, the effect is saturated.

In the present invention, since Al deoxidation is not performed,
Al is mixed as an unavoidable impurity and is usually less than 0.01%, but is preferably as low as possible.

Furthermore, in the present invention, since Si, Mn, and Cr, which are the main strengthening elements of the pearlite structure, are restricted, in order to secure the strength under these restrictions, heat immediately after the rail forming and rolling is used, or After reheating, it is effective to accelerate cooling of the front section of the rail. The cooling condition at this time is 8
The temperature between 00 and 500 ° C is preferably 1 to 5 ° C / sec. As described above, in the present invention, Si, Mn, Cr
The formation of oxides is suppressed, and the hardness is H
A good high gas pressure contact rail of B220 to HB300 can be obtained.

[0023]

EXAMPLES The effects of the present invention will be specifically described below with reference to examples. Here, the gas pressure weldability was evaluated by preparing a rail pressure welded joint under the following gas pressure welding conditions, and forcibly breaking the joint by three-point bending with a distance between two points of support of 1000 mm so that the head becomes tensile. Then, the existence of defects due to the low-melting-point oxide in the fracture surface was observed and evaluated. For gas pressure welding, a general-purpose gas pressure welding machine called TGP-HA was used, and the pressure was 58.84MP.
a (600 kgf / cm ² ), and the oxygen gas has a primary pressure of 0.68
6MPa (7.0kgf / cm ² ), secondary pressure 0.490MPa
(5.0 kgf / cm ² ), the flow rate was 115 L / min, and the acetylene gas was 0.127 MPa (1.3 kgf / cm ² ) in primary pressure.
Secondary pressure 0.059MPa (0.6kgf / cm ² ), flow rate 12
The test was performed under the conditions of 5 L / min.

Table 1 shows the chemical components of the test rail. References A to F are rails of the present invention, and GI are comparison rails.
For each test rail, perform gas pressure welding under the above conditions,
Table 2 shows the results of visually evaluating the occurrence of defects in the gas pressure welded joint. As is clear from the table, no welding defects were observed in the rail of the present invention.

[0025]

[Table 1]

[0026]

[Table 2]

[0027]

According to the present invention, it is possible to prevent the generation of oxides and low melting point composite oxides (mullite) at the pressure contact interface during gas pressure welding of rails, and to prevent the occurrence of defects such as cracks caused by the products. Perlite rails can be provided.

Claims (6)

[Claims] 1. A mass% containing C: 0.60 to 1.20%, Si: 0.20% or less, Mn: 0.40% or less, and Si + Mn: 0.50% or less, with the remainder being Consisting of iron and unavoidable impurities,
A high gas pressure contact rail having a hardness of HB220 to HB300. 2. The composition according to claim 1, further comprising: Cr: 0.01 to 0.20%, and Si + Mn + Cr:
The high gas pressure contact rail according to claim 1, which contains 0.50% or less. 3. The high gas pressure contact rail according to claim 1, further comprising Mo: 0.01 to 0.50% by mass%. 4. The method according to claim 1, further comprising one or more of 0.05% to 1.00% of Cu and 0.05% to 1.00% of Ni in mass%. The high gas pressure contact rail according to any one of the above items. 5. One or more of Nb: 0.005 to 0.05%, V: 0.01 to 0.20%, and Ti: 0.005 to 0.050% by mass%. The high gas pressure contact rail according to any one of claims 1 to 4, wherein the rail is contained. 6. The high gas pressure contact rail according to claim 1, further comprising Co: 0.1 to 2.0% by mass.